1. Field of the Invention
The present invention relates to a multiple variable valve lift apparatus. More particularly, the present invention relates to a multiple variable valve lift apparatus to mitigate impact generated during changing valve lift.
2. Description of Related Art
Generally, an internal combustion engine receives fuel and air into a combustion chamber and generates power by combusting the fuel and the air. Herein, an intake valve is operated by drive of a camshaft, and air flows into the combustion chamber during when the intake valve is open. In addition, an exhaust valve is operated by drive of a camshaft, and air is exhausted from the combustion chamber while the exhaust valve is open.
Meanwhile, optimal operations of the intake valve or the exhaust valve are determined according to rotation speed of the engine. That is, lift and open/close timing of the valves are properly controlled according to rotation speed of the engine. A plurality of cams may be disposed at a camshaft such that a valve is operated by various lift for realizing suitable valve operation according to rotation speed of an engine.
In case that the plurality of cams are provided so as to drive the valve by various lift, the valve lift is changed as a cam portion forming a high cam and a low cam is moved along an axial direction of the camshaft such that a high cam or a low cam is selected according to situation. For example, a guide rail is formed at the cam portion or an operating unit moving the cam portion along an axial direction of the camshaft, and a pin is selectively inserted into the guide rail, and the valve lift can be changed according to the cam portion or the operating unit is moved along an axial direction of the camshaft by relative movement of the pin with the rotation of the camshaft.
At this time, impact may be generated at the moment that the pin to be guided by the guide rail is inserted into or contacted to the guide rail. Further, the impact generates noise and aggravates stability of changing valve lift.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.